This module constitutes in effect the 'main' class of the nexml schema. It defines the complex type for the root <nex:nexml> element and a simple type for the schema "version" attribute of the root element. In addition, this module includes the main schema modules for OTUs, characters, trees and metadata. The data type definitions in these included schema modules are then used to define element instances in the child substructures of the <nex:nexml> root element. This simple type is the fixed version value, which in this iteration must be constrained to 0.9 (and will be incremented in future versions). The root element for nexml.